1. Field of the Invention
The present invention relates to an image sensor and an image sensor driving method, and the present invention relates to, for example, a CMOS image sensor and a CMOS image sensor driving method.
2. Related Art
Development of a CMOS (Complimentary Metal-Oxide Semiconductor) image sensor has been underway as an image sensor expected to replace a CCD (Charge-Coupled Device). The CMOS image sensor at low voltage with advanced function can be realized since both a logic circuit and an analog circuit can be formed integrally on the same chip (system integration can be made). On the other hand, the CMOS image sensor has a problem that global exposure cannot be performed differently from the CCD since signals are accumulated to correspond to pixels and read in series.
In recent years, a combination of column parallel A/D conversion and digital CDS (correlation double sampling) has enabled high speed imaging and low noise reading. However, even with the column-parallel digital-CDS A/D conversion technique, if power supply voltage falls, a D/A conversion lamp wave employed in A/D conversion cannot be sufficiently made large because of adoption of microfabrication process. This disadvantageously causes deterioration in S/N ratio.